Cardinal Math

Three-digit subtraction with regrouping · sheet 5 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 708 − 310 398 408 zero minus a number is zero418 smaller from larger or zero minus a number is the number498 borrows, but never pays
2 835 − 636 199 201 smaller from larger209 borrows, but never pays
3 805 − 297 508 608 borrowing through a zero618 borrows, but never pays692 smaller from larger
4 965 − 278 687 713 smaller from larger797 borrows, but never pays
5 801 − 205 596 604 smaller from larger606 borrows, but never pays696 borrowing through a zero
6 520 − 447 73 127 smaller from larger183 borrows, but never pays80 zero minus a number is zero87 zero minus a number is the number
7 476 − 177 299 301 smaller from larger309 borrows, but never pays
8 747 − 164 583 623 smaller from larger683 borrows, but never pays
9 758 − 139 619 621 smaller from larger629 borrows, but never pays
10 999 − 878 121 no pattern to catch here
11 875 − 681 194 214 smaller from larger294 borrows, but never pays
12 550 − 375 175 180 zero minus a number is zero185 zero minus a number is the number225 smaller from larger285 borrows, but never pays
13 980 − 476 504 510 zero minus a number is zero514 borrows, but never pays516 smaller from larger or zero minus a number is the number
14 247 − 137 110 no pattern to catch here
15 505 − 234 271 301 zero minus a number is zero331 smaller from larger or zero minus a number is the number371 borrows, but never pays
16 304 − 114 190 200 zero minus a number is zero210 smaller from larger or zero minus a number is the number290 borrows, but never pays
17 632 − 605 27 33 smaller from larger37 borrows, but never pays
18 202 − 104 98 102 smaller from larger108 borrows, but never pays198 borrowing through a zero
19 378 − 190 188 228 smaller from larger288 borrows, but never pays
20 605 − 358 247 347 borrowing through a zero353 smaller from larger357 borrows, but never pays

Reading the wrong answers

One wrong answer is a slip. The same pattern on three or more problems is a rule your child is following, and it has a name and a fix in the guide. Problems marked "no pattern to catch" are the plain ones; a child who gets only those right is telling you something too.

Borrows, but never pays 18 of 20 problems

Adds ten to the ones but leaves the tens alone. Looks like borrowing; the answer is ten too big.

52 − 38 they write 24 it is 14

Smaller from larger 18 of 20 problems

Takes the smaller digit from the bigger one in every column, whichever is on top. Never borrows.

52 − 38 they write 26 it is 14

Zero minus a number is the number 6 of 20 problems

When the top digit is 0, writes the bottom digit as that column's answer.

40 − 27 they write 27 it is 13

Zero minus a number is zero 6 of 20 problems

When the top digit is 0, writes 0 for that column.

40 − 27 they write 20 it is 13

Borrowing through a zero 4 of 20 problems

Turns the 0 into a 9 and gives the ones their ten, but never reduces the column left of the zero.

302 − 167 they write 235 it is 135

Not sure which? The five-minute check picks the problems that tell the patterns apart and names the one it sees.